The present invention relates in general to a display device, and, more particularly, the invention relates to a technique which is effective when applied to the gamma correction of a video signal voltage that is applied to respective pixels in a display device.
A liquid crystal display module of the TFT (Thin Film Transistor) type has been popularly used as a display device in a notebook type personal computer and the like. As this type of liquid crystal display module, a liquid crystal display module which uses polysilicon in a semiconductor layer of a thin film transistor (TFT) (hereinafter also referred to as a “polysilicon-type liquid crystal display module”) has been known.
In this polysilicon type liquid crystal display module, the following known method has been employed. That is, display data within one horizontal scanning line period is stored, reference data which is sequentially increased or decreased within one horizontal scanning line period is generated, and the stored display data and the reference data are compared. Then, when the stored display data and the reference data coincide with each other, a video signal voltage generated by a video signal voltage generating circuit is sampled and is applied to respective pixels (hereinafter referred to as “PWM method”) (see Japanese Unexamined Patent Publication JP-A-6-178238 (patent literature 1) and JP-A-11-272242 (patent literature 2)).
As the above-mentioned video signal voltage generated by the video signal voltage generating circuit, a voltage in having a voltage waveform which is in the form of an inclined wave (a so-called “ramp voltage”) is used.